I'm one of the people who get paid a lot of money to find 0.5ms gains, and yes, in this case it's hardly worth mentioning. Differences in frame time when you're sub 4ms really are not significant and are likely to be due to any number of bottlnecks which are unlikely to be present at more realistic framerates (when people like me might be more likely to care).
There's no indication here about hardware, drivers, or any number of external factors here. This is purely Valve having another dig at Microsoft in the press, because Win8 threatens their business model. There's a lot of smart people working at Valve. I'd expect better of them.